The present invention relates generally to a system for delivering medicine to a patient, and more particularly, to a system having a patient-controlled infusion pump which delivers medicine to an internal treatment site.
Pain management is an important aspect of post-operative recovery from surgery. Pain management usually begins immediately following the surgical procedure with the administration of narcotics or other pain control medications to the patient while the patient is under the direct supervision of the health care provider. The pain control medications are most commonly administered either orally or by injection.
The proliferation of less-invasive arthroscopic techniques for the surgical repair of many joint or soft tissue injuries and ailments has significantly reduced post-operative recovery times and the attendant pain experienced by the patient. The current trend toward arthroscopic techniques frequently enables surgical procedures to be performed on an outpatient basis or with shortened post-operative hospital stays. As a result, the bulk of the post-operative recovery time is spent in the home or even in the workplace. One goal of home recovery is to phase the patient back into routine physical activities relatively quickly as a means of shortening the post-operative recovery time.
Since the patient is generally not under the direct supervision of the health care provider when in the home or workplace, the responsibility for administering pain control medications falls on the patient in these environments. Nearly all self-administered pain control medications are oral medications because most individuals lack the requisite knowledge, skill, and experience to self-administer pain control medications by injection. Unfortunately, however, pain control medications administered orally are transported throughout the body and correspondingly affect the entire body, often causing undesirable side effects such as drowsiness, disorientation, nausea, constipation or vomiting. In contrast, injected pain control medications can be administered more locally than orally administered medications, thereby frequently avoiding the undesirable side effects of oral medications. In addition, injected pain control medications reach the treatment site more rapidly and in greater concentrations than oral medications, rendering injected pain control medications a more effective pain control therapy. Although advantageous, injected pain control medications are nevertheless not feasible for most individuals not under the direct supervision of health care providers for the reasons set forth above. In addition, it has been found in many instances that pain control medication is most effective if periodically injected into the treatment site as a single relatively large pulse, termed a bolus dosage, when the patient senses the oncome of discomfort due to pain rather than being continuously injected into the treatment site over time. However, if the patient is allowed to self-administer injection of the pain control medication on an as needed basis in the absence of supervision of a health care provider, the risk of overmedication is significant.
The present invention recognizes a need for a device which enables the patient to effectively self-administer medication by injection even when the patient lacks the requisite knowledge, skill or experience to perform injections. Accordingly, it is an object of the present invention to provide a medication delivery system, wherein operation of the system is controlled by the patient. More particularly, it is an object of the present invention to provide such a medication delivery system, wherein the patient controls the injection of the medication directly into a treatment site of the patient. It is another object of the present invention to provide such a medication delivery system, wherein the system can be effectively operated by a patient lacking any specific medical knowledge, skill or experience in performing injections. It is another object of the present invention to provide such a medication delivery system, wherein the system automatically prevents the patient from overmedicating oneself. It is still another object of the present invention to provide such a medication delivery system, wherein the system is fully self-contained and portable so that the system can be worn by the patient during routine physical activity. It is yet another object of the present invention to provide such a medication delivery system, wherein the system may be cost-effectively disposed after a single patient use.
These objects and others are accomplished in accordance with the invention described hereafter.
The present invention is a portable, patient-controlled medication delivery system, which enables a patient to self-administer a liquid medical treatment fluid to a treatment site. The medication delivery system includes an infusion pump and a medicine catheter. The medicine catheter has a first end, which is positionable in the treatment site of the patient, and a second end, which is in fluid communication with the infusion pump to provide fluid communication between the infusion pump and the treatment site. The infusion pump retains a total charge of the treatment fluid comprising a plurality of full or partial dosages and provides a drive mechanism for delivering one or more dosages of the treatment fluid to the treatment site.
The infusion pump has a flexible fluid reservoir, a rigid dosage chamber, a displacement piston slidably displacable within the dosage chamber, and a charge flowpath, which provides fluid communication between the fluid reservoir and the dosage chamber. The charge flowpath includes a passive flow restrictor having a fixed length and a fixed cross-section. An elastic member is also positioned in the infusion pump and connected to the displacement piston. The elastic member is transitionable from a more stressed position to a less stressed position to charge the dosage chamber with the treatment fluid from the fluid reservoir at a charge flow rate controlled by the passive flow restrictor. The fixed length and fixed cross-section of the passive flow restrictor are selected to produce the controlled charge flow rate of the treatment fluid. The elastic member is further transitionable from the less stressed position to the more stressed position to discharge the treatment fluid from the dosage chamber via the fluid outlet. The elastic member displaces the displacement piston in a first direction away from the fluid outlet to expand the dosage chamber when the elastic member transitions from the more stressed position to the less stressed position. Conversely, the displacement piston is manually displaced in a second direction toward the fluid outlet to contract the dosage chamber when the elastic member transitions from the less stressed position to the more stressed position.
The fluid reservoir is preferably a substantially inelastic bladder having a fluid capacity substantially greater than the fluid capacity of the dosage chamber. In particular, the fluid reservoir preferably has a capacity for a plurality of full dosages of the treatment fluid, whereas the dosage chamber has a capacity for only one full dosage of the treatment fluid. The elastic member is preferably a coiled spring connected to the displacement piston by engagement with a manually displacable actuator button which in turn engages the displacement piston. The flow restrictor is preferably a continuously open length of flexible tubing.
In operation, one end of the medicine catheter is placed in the treatment site and the other end is placed in fluid communication with the infusion pump. The fluid reservoir is filled with the total charge of the treatment fluid and the dosage chamber is charged with a treatment fluid dosage of the treatment fluid form the fluid reservoir. The infusion pump is mounted on the body of the patient and the patient self-administers the treatment fluid by manually depressing the actuator button. The actuator button drives the displacement piston through the dosage chamber in the second direction, while transitioning the elastic member from the less stressed position to the more stressed position. The displacement piston contracts the dosage chamber and displaces the treatment fluid dosage from the dosage chamber into the treatment site via the medicine catheter.
The dosage chamber automatically recharges with the treatment fluid when the actuator button is released. Release of the actuator button enables the elastic member to automatically transition from the more stressed position to the less stressed position, thereby displacing the displacement piston in the first direction within the displacement chamber. Displacement of the displacement piston creates a void in the dosage chamber of extremely reduced pressure relative to the fluid reservoir. The extremely reduced pressure preferably constitutes a near total vacuum. In the meantime, the fluid reservoir is maintained at substantially ambient atmospheric pressure. The positive pressure differential created between the fluid reservoir and the dosage chamber drives the treatment fluid from the fluid reservoir through the charge flowpath into the dosage chamber at the charge flow rate controlled by the passive flow restrictor. The controlled charge flow rate is preferably substantially constant and corresponds to a desired dosage rate of the treatment fluid to the patient.